Biofouling control

ABSTRACT

A system and method for stabilizing bromine in an industrial water system by monitoring and flexible dosing of chlorine oxidant and halide ion stabilizer residual levels. The system comprises chlorine oxidant, and a halide ion source with a halogen stabilizer.

FIELD OF THE INVENTION

This invention is in the field of industrial water systems.Specifically, this invention optimizes the use of halogen biocides inindustrial water systems.

BACKGROUND OF THE INVENTION

Fouling in industrial water systems occurs even in industrial watersystems treated with the best water treatment programs currentlyavailable. When fouling occurs, the water system is negatively impactedby contamination including deposition of air-borne, water- borne andwater-formed contaminants, process leaks, and other factors. If foulingis allowed to progress, the system can suffer from decreased operationalefficiency, premature equipment failure, and increased health-relatedrisks associated with microbial fouling.

Fouling can also occur due to microbial contamination. Sources ofmicrobial contamination in industrial water systems are numerous and mayinclude, but are not limited to, air-borne contamination, water make-up,process leaks, and improperly cleaned equipment. These microorganismscan establish microbial communities on any wetable or semi-wetablesurface of the water system. More than 99% of the microbes present inthe water process may be present on system surfaces.

The use of oxidizing biocides in biofouling control methods is wellestablished. Common oxidizing biocides such as chlorine and bromine areeffective biofouling control agents so long as they are maintained ateffective concentrations in the water. Unless the concentrations of thebiocides are effectively monitored, improper levels result in undesiredmicrobial growth, scaling, corrosion, environmental impact, andincreased cost that limit industrial applicability.

Developments in industrial water treatment incorporating higher pHvalues and corrosion inhibitors have driven interest in biocide systemsother than chlorine. Bromine use in biofouling control usually occursthrough addition of sodium bromide to the water system with an oxidizingagent such as chlorine gas or sodium hypochlorite. The result of thisapproach is the generation of hypobromous acid, which may require lessbiocide feed to maintain overall cleanliness than a comparable systemoperating on chlorine alone. However, many of the same compounds andconditions that reduce chlorine effectiveness also reduce bromineeffectiveness.

U.S. Pat. No. 6,110,387 (hereinafter the '387 patent) entitled“SULFAMATE STABILIZATION OF A BROMINE BIOCIDE IN WATER” to AlbemarleCorporation attempted to demonstrate the importance of manipulating theorder of addition of active components to the water to be treated.Essentially, the '387 patent discloses effective biocidal activity isachieved by introducing sulfamate and water-soluble bromide to thesystem before the chlorine oxidant is added. Uncertainty of improvedbiocidal performance, cost-effectiveness, actual stabilization, andeffects on the environment limit its application in biocidal control.

U.S. Pat. No. 6,478,972 entitled “Method of Controlling MicrobialFouling” to Acculab Co. discloses the use of hypobromous acid, HOBr,formed by the reaction between an aqueous solution of alkali or alkalineearth metal hypochlorite and a bromide ion source. The applicantsdescribe aqueous hypochlorite solution, water-soluble bromide ionsource, with sulfamate ion source as stabilizer as an improvedanti-fouling system.

Despite ongoing research, an efficient strategy for feeding effectivedoses of bromide and stabilizer to water systems being treated withchlorine has not previously been described. Thus, the multiple problemsin devising an efficient biofouling control system remain.

SUMMARY OF THE INVENTION

Effective and economical biofouling control is provided by the novel useof chlorine oxidant, a halide ion source, and a stabilizer characterizedby independently controlled dosing of chlorine and bromide mixed withhalogen stabilizer. The system is exemplified by the combined use ofsodium sulfamate, bromide ion, and chlorine oxidant in the methoddescribed below.

Control of biofouling in industrial water systems comprises: (a)providing at least one or more means to independently monitor andcontrol chlorine oxidant; (b) comparing the monitored concentrationidentified in step (a) to a predetermined concentration range accordingto the system to be treated; (c) adding chlorine oxidant at a rate andin an amount sufficient to maintain the determined biocidal effectiverange and, (d) adding stabilizer and halide ion source in amounts andrates sufficient to realize halogen levels sufficient to effect foulingcontrol in said body of water.

The method controls microorganisms in industrial water systems byconcurrent monitoring and flexible dosing of chlorine oxidant in thepresence of a bromide ion source and sodium sulfamate at concentrationssufficient to provide free and stabilized halogen biocide. Such free andstabilized halogens include free chlorine, free bromine,chlorosulfamates, and bromosulfamates.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

As used herein, the terms identified below are meant to designate thefollowing:

“Halide Ion Source” includes the bromide ion sources ammonium bromide[ammonium bromide 38%, CAS 12124-97], sodium bromide [sodium bromide,CAS 7647-15-6], lithium bromide [lithium bromide, CAS 7550-35-8],calcium bromide [calcium bromide, CAS 7789-41-5], potassium bromide[potassium bromide, CAS 7758-02-3], bromine chloride [bromine chlorideCAS 13863-41-7], bromine [bromine CAS 7726-95-6], BCDMH[3-Bromo-1-chloro-5,5-dimethylhydantoin, CAS 126-06-7], DBDMH[1,3-Dibromo-5,5-dimethylhydantoin CAS 77-48-5], DBNPA[2,2-Dibromo-3-nitrilopropionamide CAS 10222-01-2], Bronopol[2-Bromo-2-nitropropane-1,3-diol, CAS 52-51-7], and other effectivebromide sources known to those skilled in the art. “Chlorine Oxidant”means chlorine (Cl₂) [chlorine, CAS 7782-50-5], hypochlorous acid(HOCl), [hypochlorous acid, CAS 7790-92-3] or hypochlorite ion, (⁻OCl)[hypochlorite, CAS 14380-61-1].

“Chlorine Oxidant Source” means a substance or mixture of substancesreleasing, generating, or yielding Chlorine Oxidant. Examples includegaseous or liquid chlorine sources, sodium hypochlorite [sodiumhypochlorite, CAS 7681-52-9], calcium hypochlorite [calciumhypochlorite, CAS 7778-54-3], dichloro-isocyanurate[1,3-Dichloroisocyanuric Acid, CAS 2782-57-2], trichloro-isocyanurate,chlorosulfamate [chlorosulfamic acid, CAS 7778-42-9], BCDMH,dichloro-hydantoin [1,3-dichloro-5,5-dimethylhydantoin, CAS 118-52-5],or electrolytic chlorine generators.

“Halogen Stabilizer” includes sulfamic acid [Sulfamic acid, CAS5329-14-6], sodium sulfamate [Sodium Sulfamate, CAS 13845-18-6],potassium sulfamate [Potassium Sulfamate, CAS 13823-50-2], saccharine[saccharin CAS 81-07-2], benzene sulfonamide [benzenesulfonamide, CAS98-10-2], urea [urea CAS 57-13-6], ammonia [ammonia CAS 7664-41-7],thiourea [thiourea, CAS 62-56-6], creatinine [creatinine CAS 60-27-5],cyanuric acids [e.g. 1,3,5-triazine-2,4,6(1H,3H,5H)-trione, CAS108-80-5], alkyl hydantoins [e.g. 2, 4-Imidazolidinedione, CAS461-72-3], monoethanolamine [1-amino-2-hydroxyethane CAS 141-43-5],diethanolamine [2,2′-dihydroxydiethylamine CAS 111-42-2], organicsulfonamides [e.g. sulfanilamide CAS 63-74-1], biuret[imidodicarbonicdiamide CAS 108-19-0], organic sulfamates, and melamine[1,3,5-triazine-2,4,6(1H,3H,5H)triimine CAS 108-78-1]

“Stabilized Halogen” includes chlorosulfamate [chlorosulfamate CAS17172-27-9], dichlorosulfamate [dichlorosulfamate CAS 17085-87-9],bromosulfamate [bromosulfamate CAS 134509-56-1], dibromosulfamate,bromochlorosulfamate, and the bromo- and chloro- derivatives of thelisted halogen stabilizers.

“Residual Oxidant” is Halogen capable of reacting with DPD [N,N-diethyl-p-phenylenediamine CAS 93-05-0] reagent

“Chlorine Dose” is the amount of chlorine oxidant applied to the watersystem

“Stabilizer Dose” is the amount of halogen stabilizer applied to thewater system

“Stabilized Bromine” is bromosulfamate, dibromosulfamate,bromochlorosulfamate, and the brominated derivatives of the definedhalogen stabilizers.

“Biocidal Effective Range” is the concentration of oxidant required tomitigate pests in a treated water system.

“Biofouling” is undesirable sessile or planktonic organisms in a watersystem.

THE INVENTION

Halogen Stabilizer

Halogen Stabilizers are defined herein to include, but not limited to,sulfamic acid, sodium sulfamate, potassium sulfamate, saccharine,benzene sulfonamide, urea, ammonia, thiourea, creatinine, cyanuricacids, alkyl hydantoins, mono ethanolamine, diethanolamine, organicsulfonamides, biuret, organic sulfamates, and melamine. Exemplifiedhalogen stabilizers include sulfamic acid or a water-soluble sulfamatesalt. Examples of water-soluble sulfamate salts include but are notlimited to sodium sulfamate or potassium sulfamate. The stabilizerconcentration range is from about 0.01 to about 100 mg per liter.Illustrative ranges are about 0.1 to about 50 and about 1 to about 10 mgper liter.

Bromide ion Source

The bromide ion source is a water-soluble bromide salt. Examples ofwater-soluble bromide salts that may be used include sodium bromide,potassium bromide, calcium bromide, zinc bromide, ammonium bromide,lithium bromide, bromine chloride, bromine, BCDMH, DBDMH, DBNPA,Bronopol and the like. A water-soluble bromide salt is an alkali metalbromide or an alkaline earth bromide. Typically the alkali metal bromideincludes the water-soluble bromide salt is sodium bromide. The bromideconcentration range is from 0.1 to 1000 mg per liter. An illustrativerange is about 30 to about 100 and about 1 to about 3 mg per liter.

Ratio of Stabilizer to Bromide Ion

The ratio of stabilizer to bromide ion is chosen to provide effectivebiofouling control while avoiding over-stabilization. This means a molarratio of about I mole stabilizer to about 0.01 through about 100 molesof bromide ion. Illustrative molar ratios are about 1 mole stabilizer toabout 1 through about 10 moles bromide ion. Inclusive in this range is amolar ratio in the range of about 1 mole stabilizer to about 1 throughabout 3 moles bromide ion.

Chlorine Oxidant

The chlorine dose and residual oxidant concentration will vary based ondemand and the residual required to control biofouling. Residual oxidantconcentrations should range from about 10 mg per liter to 0 mg perliter. Illustrative residual oxidant concentrations range from about 5to about 0.1 mg per liter. A further illustrative range for residualoxidant concentrations range from about 2 mg per liter to about 0.2 mgper liter.

Monitoring Methods

Halogen oxidant monitoring methods include DPD, amperometric titration,FACS, Oxidation Reduction Potential (ORP), and the like.

Halide monitoring methods include ion chromatography, ion-selectiveelectrodes, and various wet chemical methods known to those skilled inthe art.

EXAMPLES

Comparative Example 1

A 27,000-gallon open recirculating cooling water system (pH 8.8)operating on a commercial building used a combination of sodiumhypochlorite and sodium bromide as a biocide program. The chlorineoxidant and bromide were blended at a 4:1 Cl₂:Br molar ratio just priorto dosing into the cooling system. The chlorine oxidant and bromidecombination was dosed to the cooling water system to maintainapproximately 0.1 mg/L residual oxidant, controlled using a Hach CL17chlorine analyzer (Hach Company, Loveland, Colo.).

Although microbial control was acceptable using this program, bromideconcentrations in the cooling system water were not cost-effective onthe low chlorine demand and low chlorine dose required for biofoulingcontrol in this water system.

To improve the biocide treatment efficiency of this cooling watersystem, a 30% sodium bromide and 10% sodium sulfamate solution replacedthe former sodium bromide product. The 30% bromide and 10% sodiumsulfamate solution was dosed directly to the cooling water system tomaintain bromide and sulfamate concentrations in the cooling water ofapproximately 0.3 mg/L and 0.1 mg/L, respectively. Dosage of the bromideand sulfamate solution was controlled by a Nalco TRASAR® (Nalco Company,Naperville, Ill.) product controller. Sodium hypochlorite was addeddirectly to the water system as needed to maintain a 0.1 mg/L residualoxidant, controlled using a Hach CL17 chlorine analyzer.

To measure the biofouling control performance of the new product anddosing method, total aerobic bacteria, anaerobic bacteria, fungi, andother microbes were measured using culture and microscopic analysis ofwater samples collected twice per week. Bromide and sulfamateconcentrations from water samples were also measured twice per weekusing ion chromatography.

Bacterial counts were maintained at or below 10,000 CFU/ml during thetest period.

Fungi and anaerobic bacteria including, sulfate-reducing bacteria, weremaintained below detection (<10 CFU/ml). Algae growth was controlled asassessed by visual inspection of sunlit areas.

The improved process and biofouling system, which incorporated sodiumbromide and sodium sulfamate to maintain 0.3 mg/L bromide and 0.1 mg/Lsulfamate in the cooling water system, illustrated that the bromideconcentration in the water system was reduced by up to 99% whilemaintaining satisfactory control of biofouling.

Example 2

Controlled tests were also performed to determine the effect of sodiumbromide and sodium sulfamate solutions on chlorine oxidant consumption,oxidant-induced corrosion, and oxidation-reduction control inchlorinated cooling water systems.

A 50-liter pilot cooling water system (pH 7.5) was treated with threedifferent halogen oxidant methods:

-   -   1. sodium hypochlorite (NaOCl) only    -   2. NaOCl and sodium bromide (NaBr)    -   2 0 3. NaOCl and NaBr plus sodium sulfamate

Sodium hypochlorite was dosed and controlled independently from thesodium bromide or sodium sulfamate dosing.

In each case, chlorine oxidant dose was controlled using anoxidation-reduction potential (ORP) meter at a 500 millivolt set point(GLI International, Milwaukee, Wis.). Sodium hypochlorite productconsumption was measured by determining the use rate of a sodiumhypochlorite product of known chlorine concentration. Sodium bromide andsodium sulfamate solution dosing was controlled by a Nalco TRASAR®(Nalco Company, Naperville, Ill.) product controller to maintainapproximately 3 mg/L bromide and 1 mg/L sulfamate in the water system.

Table 1 shows chlorine oxidant consumption for each treatment strategy.Chlorine oxidant consumption is expressed as mg of chlorine oxidantdosed per liter of cooling water blowdown. The addition of sodiumbromide to the cooling water system reduced chlorine oxidant consumption36%. The addition of sodium bromide and sodium sulfamate to the coolingwater system reduced chlorine oxidant consumption an additional 18%(total of 54% reduction) compared to the sodium bromide alone. TABLE 1Chlorine Oxidant Percent Chlorine Oxidant Program Consumption (mg/L)Oxidant Savings NaOCl only 3.9 — NaOCl and NaBr 2.5 36 NaOCl and NaBrwith 1.8 54 sodium sulfamate

Copper corrosion rates in the treated water system were measured using aNalco NCM100 Corrosion Monitor (Nalco Company, Naperville, Ill.). Usingonly sodium hypochlorite for treatment, copper corrosion rates rangedfrom 0.15 to 0.28 mpy (mils per year). When sodium bromide and sodiumsulfamate were added to this water system under independent dosingcontrol, copper corrosion rates decreased to the range of 0.00 to 0.01mpy.

“Although the invention has been described in detail in the foregoingfor the purpose of illustration, it is to be understood that such detailis solely for that purpose and that variations can be made therein bythose skilled in the art without departing from the spirit and scope ofthe invention except as except as it may be limited by the claims.”

1. A biofouling control system comprising: (a) a first compositioncomprising Chlorine Oxidant; and; (b) a second composition comprising aHalide Ion Source and a Halogen Stabilizer, with the proviso that thehalide ion is not chloride; wherein the system provides an economicmethod of biofouling control in industrial water by independent dosingof the first composition and the second composition.
 2. The system ofclaim 1, wherein the halide ion source is bromide.
 3. A method forcontrol of biofouling in industrial water comprising the steps of: (a)providing at least one or more methods of monitoring the chlorineoxidant concentration; (b) providing a chlorine oxidant source (c)providing a mixture of halogen stabilizer and halide ion source; (d)adding chlorine oxidant source identified in step (b) at a rate and inan amount sufficient to achieve the concentration range and; (e)independently adding composition (c) in an amount sufficient to achievethe halogen stabilizer concentration range.
 4. A method for control ofbiofouling in industrial water comprising the steps of: (a) providing atleast one or more methods of monitoring the chlorine oxidantconcentration; (b) providing at least one or more methods of monitoringthe halogen stabilizer concentration; (c) providing a chlorine oxidantsource (d) providing a mixture of halogen stabilizer and halide ionsource; (e) comparing the monitored concentrations identified in steps(a) and (b) to pre-determined concentration ranges according to thesystem to be treated; (f) adding chlorine oxidant source identified instep (c) at a rate and in an amount sufficient to achieve theconcentration range and; (g) independently adding composition (d) in anamount sufficient to achieve the halogen stabilizer concentration range.5. A method for control of biofouling in industrial water comprising thesteps of: (a) providing at least one or more methods of monitoring thechlorine oxidant concentration; (b) providing chlorine oxidant source(c) providing a mixture of halogen stabilizer and halide ion source; (d)adding chlorine oxidant (b) at a rate and in an amount sufficient toachieve the biocidal effective range and; (d) independently addingcomposition (c) to achieve a molar ratio of chlorine oxidant to halideion source.
 6. A method for control of biofouling in industrial watercomprising the steps of: (a) providing at least one or more methods ofmonitoring the chlorine oxidant concentration; (b) providing at leastone or more methods of monitoring the halogen stabilizer concentration;(c) providing chlorine oxidant source (d) providing a mixture of halogenstabilizer and halide ion source; (e) adding chlorine oxidant (c) at arate and in an amount sufficient to achieve the biocidal effective rangeand; (f) independently adding composition (d) to achieve a molar ratioof chlorine oxidant to halide ion source.